It's been awhile since I've read the series, so my memory's a little spotty, but the MC was using straight up magical items he gained in the eponymous dungeon; as I remember it, they screwed with the recording to make it appear as if he was just putting something in her drink. She confronted him...
There was a series I read (and eventually dropped) that touched on it, as well; most only had the two ears on the top, but some had 4 ears (two animal, two human), and it was used as a sign they were half-breeds.
Aside from the obvious reason of "so the FMLs have a reason to further seduce the MC"? Many tales equate succubi with vampires, who, when they're depicted as actual monsters and not just another fantasy race, often either kill their victim or make them thralls.
Look at the lengths simps go to...
Funnily enough, that exact thing happened in Sex & Dungeon, a manga with a vaguely similar premise; one of the girls was suspicious of the MC and how he was magically changing her friend's opinion of him, so she baited him into her room, where she had a hidden camera set up to catch him.
100%. It's already been established that they retain some semblance of memories from the time they're hypnotized the longer they're under its influence; and Aisaka's become proactive in getting involved with him even while not actively being hypnotized.
Eventually, they'll probably end up more...
Interestingly, it's not that outlandish, since the term "kung fu" originally meant any study, learning, or practice that requires patience, energy, and time to complete; it could refer to anything that could be achieved through hard work and practice, not just martial arts.
If the skill were...
Yep. The manga covered it pretty well and it works exactly as described; the main drawback, though, is it's nowhere near as strong as a regular crossbow, due to the draw weight needing to be weak enough that you can draw it back with one hand.
If the regular crossbow is a bolt-action rifle, the...
... I'm sorry, but can we just talk about the fact that the masked kidnapper was carrying a fucking Han Dynasty jian?! You basically never see those outside of Wuxia series, to the point I didn't think non-sword folk even realized they existed.